Bit



Jan. 3, 1956 F. F. DAVIS ET AL 2,

BIT

Filed Jan. 18, 1952 5 Sheets-Sheet 2 N VEN TOR5 B) WW6 WWW ATTORNEYS United States Patent This invention relates to bits for drilling-inrock and similar hard formations, particularly to core bits for rotarydrills. The invention may be further characterized as relating to bits utilizing hard cutting, granules, such. as

diamond, tungsten carbide, or the like, as the cutting.

The present invention is a continuation-impart of. applicants cop'endin'g application Serialf No. 151,484 filed Marc'h.2 4,- 1950,,now Patent No: 2,662,738.

The drilling oi hard rock formations, particularly exploratory drilling, blast hole drilling and the like, is usually accomplished atthe present time by meansof bits that are set with hard cutting granules; For the most part the hard cutting granules used at. the present time are diamonds, although: other hard materials, such as black carbon, which is another form of industrial diamond, tungsten carbide and the like may be used, depending upon' the hardness of the formation to be penetrated. The diamonds that are used for this purpose are sometimes designated bort, these being. the imperfect stones unsuitable for gem cutting that are mined, for the most part, in South Africa.

The hard cutting granules have been used in rotary bits for many decades and for the most part they have been set in what is known as a random pattern with. the granules positioned so as to cut overlapping paths, the ideabeing, thateach of .the granules-in the bi't faceshould do an appropriate part of the work. in: reducing the hard rock formation to a pulverized mass whi'ch couldithen: be washed to the surface by the-water or drilling mud that is passed through the core-of. the drill. Sometimes the granules have been set in such overlapping. pattern: ina random setting, whereas inothe'r instances the settings have followed certain patterns, such. as radial, spiral, concentric, etc;, but in every instance the position and size of the cutting granules has been such. that all of. the rock against which the bit face is pressed during: the drilling operation, is ground: away by atileast some portion of one of the cutting granules in the bit face as the bit revolves;

We have discovered that better, results in the form of greater speed, increased rate of penetration of the drill,

greater footage per bit and. reduction inbit costs per foot of depth can be accomplished: by setting the hard cutting granules, such as diamonds; in concentric paths and by V the cut made bythe granules in one concentric path does not overlap the cut made by granules: in another con centric path. As a result of our improvements, a considerable portion of the rock which is removed is never touched by any hard" cutting granule at all, but is chipped or fractured away, without having. ever; been. cut or abraded. As a resultthecutting granules last. longer, the bit cuts faster andtthe bit costs are reduced,

It is an. objectof the present. invention. to provide an.

improved bit structure for drilling in.v hardv formations.

such as rock, concrete-and the lilie. It is a riurther ob ject of the invention to provide an improved bit strucspacingsuch concentricpaths:insuch a way that 2 ture for drilling in rock and the like hard formations, wherein cutting granules are" used and in which such granules are of a size and are positioned in arcuate tracks so as not to" cut overlapping paths.

It is a further object of. theinvention to provide an improved bit for drilling in rock and thelikehard formations, wherein by the use of the hit some of the stone is abraded away byhard cutting granulees and some is chipped or fractured away without being abraded or cut.

It is a further object of theinve'nt'ion to provide an improved core bit for: drilling: in rock and the like formations wherein the cutting granules are positioned along paths concentric with the axis of the bit, the bit being elsewhere devoid of hard cutting granules.

Other and further objects ofthe invention are those inherent in the apparatush'erein illustrated, described and claimed.

.The invention is illustrated with reference to thedrawings in which. corresponding numerals refer to the same parts and in which Figure 1 is a bottom plan view of a bit made in: accordance with the present invention showing the principal cutting: face or hit face;

Figure 2 is a sectional view longitudinally of the bit and taken along the section: line: 2-2 of Figure 1;

Figure 3 is an enlarged fragmentary view of a partof the bit face correspondingt'o the bit shown in Figure 1;

Figure. 4 is an enlarged sectional view taken along the section lines andi'n the direction of arrows 4--4' of Figure 3;

Figure 5 is" an enlarged fragmentary view similar to that shown in Figure 3. showing a part of the bit face but of a slightly modified form of setting made in accordance with the invention;v

Figure 6 is a sectional view taken along the line and in thedirection' oi? arrows 6-6 of Figure 5;

Figure 7 is an enlarged sectional view showing the manner of formation of the bits o'ftthe present invention, illustratiuga part of the' mold in which the bit is sintered, with. the bit in place" therein;v

Figure 8 is a fragmentary plan view of a portion of the mold, that part at the left of the radius 8 --8 illustrating the mold. before the hard cutting granules are placed therein during the processof bit manufacture, and that portion to the right ofthe radius 8-8' illustrating the cutting granules'laid in: the mold and before the matrix material is placed therein priorto'sintering;

Figure 9 is: a fragmentary viewof the bit face of a slightly modified form of the invention;

Figure 10 is a sectional: view,-. along the line and in v the direction of arrows l0-10'of Figure 9;.

Figure 11 is a'correspondingsectional view taken along the line and in. the direction of arrows 11-41- of Figure' 9';

Figure 12 is a merely illustrative plan view showing the operation of the cutting granules against the rock formation, inaecordance with the present invention; and

Figure 1 3 is an illustration. in vertical section showing a slightly modifiedfonn of bit used for reaming or coring.

- Figure 14 is a-- longitudinal section through a plug bit utilizing. the instant invention.

Referring, to Figures. 1 and 4', there is illustrated an exemplary form of bit made in accordance with the present invention. In this-bit there is provided at 10 a cylindrical section of tube; which is usually made of high quality steel. The tube has an outer surfacell and an inner surface 132, bothofi which. are cylindrical about the axis CL of: the bit. Inthe trade, the-cutting endot the bit is designated the bittfacef this end being shown in Figure land illustrated opposite the bracket 13' in Figure 2. The opposite endof. the bitis known as the coupling end which is illustrated opposite the bracket 14 in Figure 2. The coupling end is provided with either right or left hand threads, according to drill rotation and ianufacturers standards. The central wall 12 of the bit is generally blended into a conical wall at 15 which thins out to the lower end 16 adjacent the end of the coupling. The coupling portion 14 which has the threads 17 on it is usually screwed into what is known as the reaming shell in the drilling operation and above the reaming shell there is attached the core barrel where the drill is used for core drilling, and above the core barrel there is screwed on the tubes which are known in the trade as drill rods, or collectively as the drill string. They are actually tubes of finest quality steel, the axial opening through them being provided for the passage of water or drilling mud downwardly during the drilling operation. This trade terminology will be adhered to in this specification.

According to the present invention die bit face 13, Figure 1, is provided with a plurality of ridges concentric about the axis of the bit. In Figures 1-4 these ridges are designated 20 for the outer ridge, 21 for the inner ridge and 22, 23 and 24 for intermediate ridges. Three intermediate ridges are shown, but any number from zero to several may be used. The outer ridge 20 is closely adjacent the outer cylindrical surface 11 of the bit. The inner ridge 21 is likewise closely adjacent the inner cylindrical surface 12 of the bit, where the bit is a core drill. Each of the ridges 20 and 21 protrudes in the direction of drilling outwardly from the general surface level of the bit face. Thus, in referring to the enlarged sectional view, Figure 4, the general surface level of the bit face may be illustrated by the line 2525 and it will be observed that the outer ridge 20 protrudes in the direction of drilling from such surface 25-45, the inner ridge 21 being likewise so elevated. According to the pattern of setting of the illustrated bit in Figures 1-4 the intermediate ridges 22, 23 and 24 project a lesser amount in the direction of drilling from the general level 2525 of the bit face and accordingly such ridges 22-24 project a lesser amount in the direction of drilling that do the ridges 20 and 21.

The present invention is illustrated by a showing of core drills but it is equally applicable to plug bits wherein the surface 12 vanishes at the center line of the bit and in which case a water channel is provided at or near the center line of the bit at the coupling end, but is terminated by angle bores into the cross water channels 2626 in the bit face, as shown in Figure 14. Therefore, while the bits herein illustrated are especially suited for core drilling, it will be appreciated that the invention has applicability to plug bits and that the radius of the cylindrical inner surface 1.2 relative to the outer cylindrical surface 11 may be as desired.

According to the present invention each of the ridges 20 through 24 are concentric with the axis CL of the bit and are spaced from each other. Then along the crest of each ridge there are set a plurality of cutting granules. Thus, in the outer concentric ridge 20 there are provided cutting granules 2727 at substantially even spacings. These cutting granules are of a size such that they extend more than half way across the dimension of the ridge 20, or in other words they are of substantial size and occupy a predominate fractional proportion of the transverse dimension of the ridge 20. However, the granules 2727 are placed in substantially tracking relation. Referring to Figure 4 it will be observed that the granule 27 in the ridge 20 has certain points 27A, 27B and27C which intersect the line defining the ridges 20. It will be recalled that these cutting granules are of irregular shapes, as found in nature, and they are utilized in their natural condition. In the preferred method of manufacture, the granules are simply placed in a mold having a groove shaped to the dimension of the ridge desired to be formed and are dropped down into the bottom of such groove. As a consequence the granules seat themselves with their outermost points 27A, 27B and 27C in contact with the groove walls in mold surface, but other surfaces of the granules are spaced out of contact with the mold. Not all granules will have points contacting both sides of the groove, and where a choice is afforded the granules are placed to touch at 27A and 27C so as to hold the gauge of the resultant hole. Then, as hereinafter described, the matrix material is introduced into the mold which embeds the granule and in so doing forms the ridge, with the result that only points of the granules reach out as far as the surface of the ridge when the bit is finished. However, as the bit is used these points take a slight projection out beyond the surface of the ridge in which the granules are set, due to the wearing down of the matrix material of the ridge in which the granules are held. Consequently, the points on the granules do in service achieve a slight projection beyond the surface of the ridge in which they are embedded.

Similarly, referring to Figures 1 and 4, in the ridge 21 there are positioned granules 28 which, as illustrated in Figure 4, have points 28A, 28B and 28C coextensive with the surface of the ridge. Similarly, in each of the ridges 22, 23 and 24 there are likewise set granules in substantially tracking relation. Thus, in the ridge 22 there are provided granules 29, which are set in the crest of the ridge 22. Likewise, in ridge 23 there are set granules 30, which are in substantially tracking relation, and in ridge 24 there are provided granules 31 likewise in substantially tracking relation. As noted from Figure 4 the granules 29 of ridge 22 likewise have one or several points of contact coextensive with the surface of the ridge 22, there beingltwo such points of contact here illustrated at 29A and 29B. Similarly, in respect to ridge 23 the granule 30 has points 30A and 30B coextensive with the surface of the ridge 23, and the granule 31 has points 31A and 31B coextensive with the surface of the ridge 24.

The hard cutting granules set in tracking relation in one ridge are preferably located so as not to be radially opposite the granules in the next ridge but are staggered slightly. Thus, as shown in Figure l, granule 27-1, 27--2, etc. in the outer ridge 20 are not directly radially opposite granules 291, 292 etc. in ridge 22, but are staggered, and the latter are not radially opposite granules 30-1, 30--2, etc. of ridge 23, but are likewise staggered. This is true so far as obtainable for the setting of all the cutting granules of all ridges across the bit face. Of course, there are usually a few more granules on the outer ridges of greater circumference, and this circumstance sometimes slightly upsets the staggered arrangement, but such arrangement is in the main adhered to.

In each of the ridges the granules are thus set in sub stantially tracking relation and the granules are of a size so that the tracking granules in one ridge cut a path which is spaced from the cutting paths of the granules in each adjacent ridge. Accordingly, the cutting granules 27 cut a path corresponding to the ridge 20 and such path or groove (in the rock formation) is spaced from the path (groove) cut by the granules 29 in the ridge 22. Likewise, the cutting granules 29 in the ridge 22 cut a path or groove (in the rock formation) which is spaced from not only the path cut by the granules in ridge 20 but also spaced from the path cut by the granules in ridge 23. The same is true in respect to the path cut by the granules in ridge 23, this path being spaced from the path cut by granules in ridges 22 and 24 and similarly for 24 and 21.

Accordingly, the granules in each ridge are in substantially tracking relation and they cut grooves in the rock face which are concentric with the bit axis. Furthermore, the grooves cut by the granules in each ridge are spaced from the grooves cut by the granules in each adjacent ridge. A further characteristic of the bit is that the cutting granules in each ridge are of a size such that their cutting paths do not overlap the cutting paths of the granules in any other ridge. Thus, by reference to Figure 4,. it can be seenv that the granule 28, while cutting a distinct .path, does not in any way overlap.- the cut made by the granule 31,, nor does the cutting path of granule 31 in any way overlap. the path cut by granules 30 or 28. The same is true of the cutting granules in each of the other ridges, for in no case do the cutting paths of the granules in one ridge overlap the paths cut by the granules in adjacent ridges. Accordingly, a considerable portion of rock is left wholly untouched by the cutting granules in any ridge and the removal of this rock is due, itis. believed, to the following action which is, however, merely our theory and is in no way to be construed as a limitation upon the invention:

Referring to Figure 12 there are illustrated several exemplary cutting granules in the several concentric ridges of an illustrated bit. Figure 12 is illustrative of any of the bits of the present invention and may be considered as a fragmentary view of any of the bits illustrated in the drawings herein. Thus, the outer cutting granule O, which is in outer ridge, has a certain size and dimension and in moving in the direction of rotation R such cutting granule O scours or abrades away a path shown by the dimension 32. Similarly, the first intermediate cutting granule A has a dimension such that it scours or cuts a path illustrated by the dimension 33. The next intermediate cutting granule B cuts a path illustrated by the dimension 34. Likewise, the third intermediate cutting granule C cuts or scours a path indicated by the dimension 35. The innermost cutting granule on the inside ridge cuts or scours a path indicated by the dimension 36. In this view, of course, the cutting granules O, A, B, C and I are illustrative of other correspondingly designated cutting granules in their same respective ridges.

It will be observed that there is a certain space which is designated S1 between the dimensions 32 and 33, which is left untouched by the cutting action of any stones in any ridge. Similarly, there is a space S2 between the dimensions 33 and 34, a space S3 between the dimensions 34 and 35, and a space S4 between the dimensions 35 and 36. In each of these spaces the rock or other hard formation is untouched by any cutting granule and one might at first suppose that this would be a disadvantage. Yet, when our bits are used, we have found that for a given size of bit, penetration of the bit proceeds more rapidly than with prior art random set bits. The total footage per bit much exceeds that of customary random set bits, and the 'bit cost per foot is lower. An examination of the cuttings from our bits leads us to believe that the cutting action takes place due to combination of abrasion and fracturing of the hard rock, the abrasion taking place in. that frontal area coextensive with the aggregate radial width of the. concentric paths of the concentrically set stones of the ridges and the fracturing taking place in the spaces S 1, S2, S3 and S4 between the concentric ridges. The. motion. of the hard cutting granules in scouring or abrading concentric grooves in the rock face by applying pressure to the grooves in the rock face, appears to fractune or weaken the rock adjacent. the groove. Then when the staggered (and hence trailing granules) in adjacent ridges subsequently moves along it exerts a similar fracturing, and weakening force but. in an opposite direction,

with the result that. the rockis; cracked and fractures by side pressure, which is successively exerted first in onedirectionand then in the other direction transversely across the intervening ridges in the rock. face (between the concentric cutting granules) and. as a result the rock is cracked. and chipped off in the spaces S1 through S4. Accordingly, this part of the total rock that is removed is not worn away as in prior bits, but is merely cracked, shipped and broken away. A substantial percentage of the rock. removed thus appears to be broken (fractured) to the: .freetfaces of adjacent: grooves.

r- From another viewpoint. it maybe rationalized that the cutting action takes place on a surface which is not planar but is undulent ,(due to the. irregularities constituting the projecting concentric ridges in the rock face) and the pressure of each cutting granule against the rock is accordingly exerted across a projection of stone (transversely of the ridges) with. the result that there is a shearing force against the projecting stone quite apart from any wearing awayaction, this force being exerted successively in oppositev directions. and the stonev is fractured to a free face without abrasion being required by direct cutting ac tion of the cutting granules. The foregoing theories must be understood merely as our best present understanding of the operation of our bits and are not limitations on the invention.

In Figures 1-4 the bit illustrated is provided with the usual water channels 26-Z6 which extend across the bit face from the inner surface 12 to the. outer surface 11. Where the bit is of the plug bit. variety (and the surface 12 vanishes), these water channels may be set in the form. of a cord across. the bit face and the water supply brought out into the water channel 26. In plug bits, of course, the concentric ridges are carried to successively smaller diameters and a final stone is set in the middle, as shown in Figure 14.

The number and location of water channels depends generally upon the size of the bit and the character of the rock formation in which the bit is used. Generally a greater amount of water is required for soft formations than for hard formations, although this is not always the case. The water channels have a depth D, as illustrated in Figure 2, and at the outer end of the water channel the bit is preferably ground off along the surface E, Figure 2, so as to provide a ready flow of. the cooling water or drill mud up alongthe outer surface of the bit, reaming shell and drill string, in the direction of arrow U (which is opposite to the drilling direction), it being understood that the water or drilling mud is always pumped down the center of the drill. string and returns along the outside of the bit. In the bit illustrated in Figures 1-4 a slight radial projection is provided at the bit face of the matrix material M, both outward and inward from the surfaces II and 12.. Thus, as. shown in Figure 4, the matrix material M projects to the surface 11A by an amount P which represents clearance of the surface 11 of the bit from the hole drilled by the bit face. Similarly, a like clearance P is generally allowed between the surface 12 on .the inside of the bit and the surface 12A, so as to allow clearance betweenv the core which is cut and the inner surface 12. It is through this clearance that the cooling fluid must pass to the bit face. Roaming stones, known in the trade as kickers may be set as at K1 and K2, but their use is not always essential, since the outer and inner ridge stones 27 and 28, particularly points 27C and 28C are frequently enough to hold gauge.

' In the bit illustrated in Figures 1-4 there are three intermediate ridges 22, 23 and 24 shown, but it will be appreciated that for a very narrow out such intermediate. ridges'may be omitted and only the two outer ridges 20 and '21 used. Likewise, where desired more or less than three intermediate ridges may be used. For most bits, however, in practical drilling operations two through five intermediate ridges are preferred.

Referring to Figures 5 and 6 there is illustrated a slightlymodiii'ed form of/the invention wherein the outer ridge 4t) and the inner ridge 41 have substantially the same amount of projection from the average level 4242 of the bit faceas do the intermediate ridges 43, 44 and 45-. Stated another way, in this bit. there are a plurality of ridges across the bit face, all of the ridges being concentric with the bit axis and all having substantially equal projection in the drilling direction beyond the general level of the'bit face. In each of such ridges there are set hard cutting granules or stones,v the granules in any one ridge being in substantially tracking relation and of a size suchthat the cuttingipath of the granules in one ridge do not intersect the cutting paths of the granules in any other ridge. Thus, the granules 46 in ridge 40 do not overlap the cutting paths of the granules 47 in ridge 43, nor do the cutting paths of the granules 48 in ridge 44 overlap the cutting paths of the granules 47 in ridge 43 or that of granules 50 in ridge 45. Similarly, the cutting paths of the granules 50 in ridge 45 do not overlap the cutting paths of the granules 48 in ridge 44 nor that of the granules 51 in ridge 41.

A further characteristic of all bits made in accordance with the present invention, as illustrated by the bit shown in Figures .and 6 and also in the remaining views, is that those portions of the ridges between the crests (namely, the valleys between the concentric ridges) are completely devoid of any cutting granules. Thus, referring to Figure 1, in the space at 53 between ridge and ridge 22 there are no cutting granules whatsoever. Similarly, there are no cutting granules in the space 54 between ridges 22 and 23, in the space 55 between ridges 23 and 24, or in the space 56 between ridges 24 and 21. This is a further characteristic of our bits. The cutting granules are of a size and positioned in the concentric ridges for the especial purpose of leaving some of the hard rock against which the bit revolves free from contact with any cutting granule.

The size of the hard cutting granules as compared to the width of the ridges in which they are positioned is such that approximately to 75% of the formation in which the bit turns remains unabraded, and is fractured off as previously explained. We prefer to abrade 40% to 60% of the formation, leaving the balance to be fractured. Stated another way, the sum of dimensions 32, 33, 34, and 36 would be from 75% to 25% of the dimension H, Figure 12, and the sum of dimensions S1, S2, S3 and S4 equals 25 to 75% of such dimension H.

Referring to Figures 9, 10 and 11 there is illustrated another form of setting of our bits which comes within the aforesaid specification. In these figures the bit face is divided into several sectors. Thus, there are provided sectors 59 (of which a portion is shown), sectors 60, 61 and 62 (of which the entirety of each is shown) and a sector 63 (of which only a portion is shown). The entire circumference of the bit face is accordingly divided into a plurality of sectors, preferably even in number. In these sectors all ridges are concentric with the bit axis, but their radii are from ridge to ridge varied. The outer and inner ridges are preferably repeated in each sector, though not necessarily. It is preferred to have every other sector identical, using two patterns. Thus, sectors 60 and 62 are preferably made identical. If desired, however, three or more patterns may be used, especially for big bits. Thus, sectors 60 and 63 may be made identical with sector 62 corresponding to the sector preceding 59 and sector 61 corresponding to the sector which is the second preceding sector 59.

As illustrated, however, alternate sectors are identical. Thus, sector 60 is identical with 62; sector 59 is identical with 61 and 63. According to this pattern of bit setting there are, as previously stated, a plurality of ridges in each sector, each of which ridges being an arc concentric with the axis (CL) of the bit. As illustrated each of the sectors includes one ridge closely adjacent the outer surface 65 of the bit and another ridge closely adjacent the inner surface 66 of the bit. Thus, in all of the sectors there is a ridge 67 which is at the outer surface 65 and another ridge 68 at the inner surface 66. However, in sector 60 and sector 62 there are provided spaced intermediate concentric ridges which do not, however, track with the spaced intermediate concentric ridges in the sectors 59, 61 and 63; Thus, in sectors 60 and 62 there are provided ridges 70 and 71 which are both concentric about the axis of the bit but are spaced so as to follow the valley 72 and the valley 73, respectively, between the ridges 74 and 82 in the sectors 61, 59-and 63, the spacing in 61 being the same as in 59 and 63 as previously stated.

Each of the ridges is set with cutting granules which are set on substantially tracking relation along the arcuate ridge. However, the cutting granules are of such a size, as previously stated, so as not to protrude into or perform any cutting Work in the valleys between the ridges. Thus, the cutting granules 75 in the concentric arcuate ridge 68 are set in substantially tracking relation, but they are of such a size that they do not project into or overlap the cutting paths of the cutting granules 76 of the adjacent ridge 70, nor do the granules 76 of the ridge 70 project into or overlap the cutting paths of the granules 77 of the ridge 71. Similarly, in sector 61 the granules 75 in the inner concentric ridge 68 are of a size such that they do not project into or overlap the cutting paths of the granules 76 in the ridge 70 of sector 60. Instead, the granules 76 of ridge 70, sector 60 cut along the ridge of rock formation, which is left uncut due to the radial spacing between the ridges 68 and 74 of segment 61. Likewise, the granules 78 in the arcuate ridge 74, sector 61 (also sectors 59 and 63) are all concentric about the bit axis and cut in substantially tracking relation, but they are spaced from and do not overlap the cutting paths of any other ridge in adjacent sectors. They do, however, move along a path which is defined by the line 79 which is the ridge in the rock face which is between the cutting paths of granules 76 of the ridge 7t) and the granules 77 of the ridge 71. Accordingly, it may be stated in respect to the intermediate ridges of the bit illustrated in Figures 9, l0 and 11, that the setting of the hard cutting granules is such that all of the granules in any one arcuate ridge (repeated in successive alternate sectors) are in substantially tracking relation along the crests of such concentric ridges in which they are situated, but that the granules of each ridge are of a size and the ridges in successive sectors have spaced radii such that the cutting path of one ridge in one sector does not overlap the cutting paths of the granules in ridges of different radii in the bit, but instead, comes along the space between such ridges of different radii. The cutting paths of the granules in at least the intermediate ridges in successive sectors are spaced between the cutting paths of the granules in ridges of next proximate radii in adjacent sectors. Accordingly, the cutting granules in any ridge are positioned and have a size such that their cutting paths do not overlap the cutting paths of the granules in ridges of adjacent radii in adjacent sectors but come between them.

The cutting action of the bit shown in Figure 9 is illustrated in Figures 10 and 11 which actually are illustrations in section of the mold in which the Figure 9 bit is sintered. These figures'also approximately show the way the bit cuts when rotated, in which case the mold portion MO would be the rock formation. With this in mind it will be observed that the cutting granules 80 in the outer ridge 67 and granules 75 in the inner ridge 68 each cut a groove as at 80A and 68A. In Figure 10, however, it will be observed that the cutting granules 81 of the ridge 82 line up (radially) with the ridge 83 in the rock face which is left between the cutting granules 80 of outer ridge 67 and the cutting granules 77 of ridge 71. Similarly, the cutting granules 77 of ridge 71, Figure 11, lines up (radially) with the ridge 84 in the rock face which is left between the cutting granule 81 of the ridge 82 and the cutting granules 78 of the ridge 74. Similarly, the cutting granule 78 of the ridge 74 lines up (radially) with the ridge 85 in the rock face which is left between the cutting granule '77 of ridge 71 and the cutting granule 76 of the ridge 70, and the granule 76 of ridge 70 in turn lines up (radially) with the ridge 86 in the rock face, which is between the path cut by granule 78 in ridge 74 and the granule 75 in the innermost ridge 68. Therefore, insofar as the intermediate ridges are concerned in the bit setting of Figures 9, 10 and 11, the granules set in substantially tracking relation in each of the arcuate concentric ridges of each sector and such granules cut or plow a path down the rock ridge which is left between the cutting paths of the substantially tracking cutting granules in adjacent concentric ridges of the next preceding sector. Yet the spacing of all ridges of all sectors and the sizes of the cutting granules in them is such that substantial spaced concentric areas in the rock face are never touched by any hard cutting granule of any sector and the rock in such areas is sheared or broken away as previously explained. This breaking away of the rocks between the ridges which may be designated as breaking to a free face is a characteristic feature of operation of our bits, and occurs as previously described with reference to the bit shown in Figures 1-6.

Referring to Figures 7 and 8 there is illustrated one method which may be used for setting our bits. It will be understood, of course, that the bits may be hand set, although this method is relatively expensive and is not preferred on account of cost factors. According to the modern methods of bit setting, as exemplified in British Patent 453,344, the bit may be fabricated by disposing the cutting granules in predetermined pattern against the surfaces of a mold, after which material capable of being sintered when heated, is introduced and is impacted against and fills the entire mold void, thus embedding substantially all of the cutting granules. The steel shank of the bit, which is ultimately machined with the thread coupling 14 is then placed against the sinterable material, either with or without a tongue and groove connection into the sintered material, as desired. We have found that the sintered material sufiiciently adheres along the surface A so as not to require any tongue and groove connection, although such connections may be used if desired. Then, according to such known methods of British Patent No. 453,344, the mold having the hard cutting granules positioned therein and embedded in the sinterable material, and including the shank of the bit in contact with the sinterable material, is brought to sintering temperatures and the sinterable material then hardens into a compact mass which embeds and thoroughly holds the hard cutting granules in place. In utilizing our in vention this method of bit setting is greatly facilitated. Thus, as illustrated in Figures 7 and 8, the mold MO is machined so as to provide outer wall 91 and inner wall 92 and a bottom surface 93 which has in it a plurality of concentric grooves 94, 95, 96, 97 and 98 according to the number of ridges desired across the bit face. The concentric grooves 94-98 have appropriate dimensions, and project more or less from the average level of the bit face being formed, which corresponds to the line 25-25 of Figure 4 or the line 42-42 of Figure 6. Stated another way, the concentric grooves that are machined in the bottom of the mold are the exact impression of the concentric ridges desired to be formed. Then hard cutting granules 27, 29, 30, 31 and 28, of appropriate size, depending upon the relative sizes of the grooves 94-98, are simply placed in the grooves 94-98 in the mold. The granules being of irregular shapes seat themselves with their outermost projecting points or corners in contact with the mold. Then sinterable material M is put into the mold which is suitably closed by a central cylindrical mold portion 100 (which forms the central core space of the bit) and an outer annular mold portion 101 and the bit shank 10 of steel is then seated in contact along the line 10A with the sinterable material. The amount of pressure, the degree of heat applied, and other processing features form no part of our invention, being as in the art. It is noted, however, that by virtue of the concentricity of the grooves desired to be formed in the bit with consequent reversed impression of the mold, the hard cutting granules 27, 29, 30, 31 and 28 may easily be placed in the mold grooves and need only be spaced around such grooves in which they repose. Slight indentations in the mold, made by a prick punch or small drill bit have been commonly used for locating cutting granules in many prior bit setting operations but in forming our bits this practice need not be employed unless more than usual projection of the cutting granules is desired. The cutting granules are simply spaced along each groove of the mold corresponding to the ridges of the bit and the sinterable material, which is usually in powdered form, is then filled into the mold and is impacted around each stone and goes into contact not only with the back part of the granule (away from the bit face) but also fills the space under the stone" in the groove, as at 102, 103, 104, 105, 106, 107 and 108, with the result that when the finished bit is removed from the mold the corners of the cutting granules which had contacted with the groove of the mold, during the manufacturing operation are frequently hardly visible, and it is not until the bit is run in that a greater projection of such corners of the granule becomes apparent. Of course, as the bit is used the sintered material outwardly forming the surface of the ridges of the bit face, becomes worn away gradually exposing more and more of the hard granule.

For reaming operation, however, the bit face generally is preferably made conical as shown at 25A--25A or as shown at 25B2SB, Figure 4, and the concentric ridges formed thereon. Thus, concentric ridge 20, Figures 2 and 4, may be advanced in the drilling direction beyond concentric ridge 21, or vice versa, and the concentric ridges 22, 23 and 24 etc. oriented along the thus established generally conical surface. A bit so formed is shown in Figure 13. In either case the ridge 20, being somewhat advanced in the drilling direction accentuates the action of causing the remainder of the rock to break to a free face, thus reducing the necessity for grinding away all or the rock which is removed.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that we do not limit ourselves to the specific embodiments herein.

What we claim is:

1. A bit for drilling in rock and the like formations, said bit being in the form of a cylinder having a coupling at one end and a passage lengthwise therethrough, the opposite end of the cylinder forming a drilling face, said drilling face being composed of sectors, said bit being characterized by having a plurality of arcuate ridges in said drilling face, each ridge being concentric with the axis of the cylinder, each sector including a ridge of maximum radius and ridges of lesser radii, each of said ridges of lesser radii being arcuate, concentric with the cylinder axis and having a radial dimension different from the radii of adjacent ridges in adjacent sectors of said circular drill face, and at least several hard cutting granules set in substantially tracking relation along the crests of each of said ridges, the granules of each ridge being of a size such that their cutting paths do not overlap the cutting paths of the granules in ridges of different radii.

2. The bit of claim 1 further characterized in that the ridges of maximum and minimum radii have higher crests than the ridges of intermediate radii.

References Cited in the file of this patent UNITED STATES PATENTS 1,676,887 Chamberlin July 10, 1928 1,923,488 Howard et al. Aug. 22, 1933 2,136,359 Bley et al. Nov. 15, 1938 2,371,490 Williams, Jr. Mar. 13, 1945 2,495,400 Williams, Jr. Jan. 24, 1950 2,593,229 Wallace Apr. 15, 1952 2,662,738 Davis et al. Dec. 15, 1953 

